Things we learned while driving through Canada to Alaska
(not in any particular order)

• None of our three US cell phones worked in Canada. A Walmart techie said that two of our phones use network technology that Canada no longer uses. And the plan provider of our third phone does not have service in Canada.

• We bought a smartphone with changeable SIMM card and a month of service at Walmart.

• If your US cell phone has a changeable SIMM card, you can buy a Canadian SIMM card ($10) and service with a provider (maybe $30 for a month).

• Don’t expect the service to be available all over the Yukon. It is available in the cities. But out in the boonies, not so much.

• Canadian propane tanks are larger in diameter than US tanks. The Canadian ones would not fit in our camper. The strap to secure the tank is about a quarter of an inch too short. We had to get our tank refilled, not exchanged.

• Canada has restrictions on the age of a propane tank to be refilled. Go with really new tanks if you don’t think you can put a larger (Canadian) tank in your rig.

• Costco in Canada does not take VISA (not even the US Costco VISA card). The only charge card they take is MasterCard.

• Registers at Costco and Walmart can convert Canadian dollars into US dollars (or visa versa). At Costco, I paid for our propane with US dollars. I don’t know if you can use US dollars in Walmart. We charged everything in Walmart without any problems.

• The Grande Prairie Costco is the cheapest place in town to get a propane tank refilled (according to the staff at Walmart).

• The Grande Prairie Walmart parking lot is small and chaotic. The store is fine.

• We exchanged $20 US into loonies and toonies at a Canadian bank without any fees. For the last purchase we made before leaving Canada, we used the balance of our Canadian money to make a partial payment and paid the rest with our no-fee VISA card.

• There were free RV dumps everywhere we went. Ask at the Visitor Information Centers.

• There’s a free RV dump in the city park in Watson Lake (the city with the Sign Post Forest). The Visitor Information Center let us use the potable-water spigot on the side of their building. There’s free WiFi in the Visitor Center – ask for the password.

• The Fort St John’s Walmart does not have bulk water to fill jugs. Safeway, a few blocks away, does.

• Diesel fuel is easy to find. It is about the same price as regular gas.

• Water to refill your RV tanks is easy to find. No one charged us for this water. Ask at gas stations and visitor centers.

• We took citrus fruit from the US into Canada. But were not allowed to take citrus fruit or avocados from Canada into the US – even though they were grown in the US.

• Expect to sign for all your credit card purchases.

• The Walmart in Whitehorse does not have groceries or bulk water and does not exchange propane tanks. The Save-on-Food grocery store within easy walking distance from the Walmart has both water and groceries. There is a gas station between the Walmart and Save-on-Food. This gas station refills propane tanks, and has diesel fuel and a free dump station with potable water.

• There is a paved walking/bike path along the river across the road from the Whitehorse Walmart.

• To exchange propane tanks in Whitehorse, Tags (4421 4th Ave, 867-667-2203) will exchange if the tank is less than three years old. Tags does not refill.

• My GPS converts kilometers/hour into miles/hour. However, that was no help when I arrived at a construction zone and the speed limit went from 100 kph to 70 kph. But if I multiplied the speed limit by 0.6, I’d be pretty close to the speed limit in mph. Example, 100 kmh is close to 60mph (10x6). 70kmh would be close to 42mph (7x6). These speeds are less than the correct speed but shouldn’t displease the Mounties.

• (This is not Canada but Wyoming): There are free RV dumps at the Wyoming Visitor Information Centers at both the north in Sheridan and the south in Cheyenne.

Another wise decision by the Canadians. Not just to encourage tourism but for public health. Take my state, California, we can’t close them fast enough. Don’t be sumg USFS along US 395. What do you do all winter except lock them up? Such as French Camp and June Lake. Thankfully BLM works all winter.

Once you leave Fort St. John behind, your cell towers are almost all Bell Mobility Canada until you hit the AlCan border. Google Canadian cell tower map, and it will show you roughly where they are up there.

If your US cell phone company has a roaming reciprocity agreement with Bell or Telus, your phone should work through that stretch if there's a tower nearby. We each have a dual SIM phone, and we have an AT&T (Rogers) SIM card in her phone, and a T-Mobile (Bell/Telus) SIM card in mine. Along with our Rogers Canadian SIM cards. We're covered.
We got caught up there 2 years ago without cell service until we hit Whitehorse, where we did the same thing you did, and bought a Bell based SIM card for one of the phones.
Honestly, there aren't that many cell towers up there anyway, except as you described, in/near the bigger towns.
The rest of your observations are true.

As indicated above if you have a Verizon phone that is CDMA (not their world phone) you will be out of luck here in Canada. We have an AT&T SIM card that slips into our Canadian GSM phone and AT&T pairs with Rogers here and the US SIM card works here. I understand that other US providers are also GSM with the exception of Verizon. GSM is the world standard (just like metric!).

Some CDMA is still around in some cities here but you will be lucky to connect with a CDMA phone

Along the subject line of SIM cards and cell phones in Canada - I don't know if it would help our US cousins but all new cell phones in Canada must be "unlocked" or offered to be unlocked by the seller. This means that any compatible SIM card (correct size as well) from any carrier will work in any new phone purchased up here.

"SIM locking was ultimately banned in Canada on December 1, 2017 as part of amendments to the Canadian Radio-television and Telecommunications Commission's Wireless Code. All new devices in Canada must be sold unlocked, and carriers must offer to unlock existing phones free-of-charge."

Would unlocked phones be helpful in the US? Give you more options for carrier selection? You could pop anyone's SIM card into your unlocked phone and it should work.

Yes, I've always bought unlocked smart phones here in Canada as I refuse to be locked in to a specific carrier here. In the US I have bought Sims for various carriers there, their rates are lower with much more data than I could get with a Canadian plan add on.